Southwest Anthony Henday Drive Noise Study 1 Introduction to Sound - - PowerPoint PPT Presentation

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Southwest Anthony Henday Drive Noise Study

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Introduction to Sound

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Decibel Scale

• Noise is measured using a Decibel (dB) Scale
• The Decibel Scale is a base-10 logarithm scale

(similar to Richter Scale)

– Change of 1-2 dB - threshold for subjective change – Change of 3 dB - barely perceptible – Change of 5 dB - strongly perceptible – Change of 10 dB - considered twice as loud

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Decibel Scale

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A-Weighting Scale (dBA)

• An “A-Weighting” scale (dBA) is being used to

measure sound in the SW AHD noise study

– A-weighting matches human hearing

• Human hearing is not linear at different

frequencies (i.e. pitch)

• Human hearing reduces the volume of both low

and high frequency (pitch) sounds compared to middle frequency sounds

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Fluctuating Sounds

Energy Equivalent Sound Level (Leq)

• ver a 24-hour period

Leq24 = 57.5 dBA

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Energy Equivalent Sound Level

• Over time, sound is measured using the Energy

Equivalent Sound Level (Leq)

– Takes into account noise fluctuations – A short burst of loud noise is perceived to be as annoying to the average person as sustained noise at a lower level (i.e., loud air brakes for a short time versus continuous, low- level traffic noise) – One number represents all this data over a given time period – Uses Logarithmic Average of sound (not arithmetic)

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Energy Equivalent Sound Level

• The SW AHD noise study uses a 24-hour time

period for the Energy Equivalent Sound Level (Leq)

– Sound is continuously measured by the noise monitor and the Leq is logged every 15 seconds for the entire 24- hours. – The Leq is determined largely by louder sound levels. – The purpose of this method is to reflect the way that people respond to sound.

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Factors that Affect Noise

• Certain conditions affect how noise travels and is

perceived

– Wind – Temperature – Topography – Ground cover

• These conditions influence how and when noise

monitoring can take place

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• Single biggest reason for day-to-day fluctuations in urban noise
• Decreased noise level upwind, increased noise level downwind
• The difference between sound upwind/downwind can be +10 dBA

Source Wind

Shadow Zone

Factors that Affect Noise - Wind

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Factors that Affect Noise - Temperature

• Normal gradient (i.e. colder temp. at higher

elevation) generally has neutral effect on sound

• Temperature inversion (i.e. warmer temp. at

higher elevation) can reflect sound back towards ground

• Difference can be +10 dBA
• Temperature inversion occurs when wind is calm

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Factors that Affect Noise - Temperature

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Factors that Affect Sound Travel

• Rain

– Falling rain (or snow) has little effect on sound travel – Wet road surface has different sound “quality” than dry

• Topography

– Hills can provide sound attenuation – Valleys can provide sound amplification

• Ground Cover

– Grass, grain crops, foliage can absorb sound – Snow cover can absorb or reflect sound

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Traffic Noise

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Sources

• Dominated by tire noise at speeds greater than

about 50 km/h

• Engine noise (from front grill and reflections off road)
• Exhaust noise (higher up for large trucks and busses)
• Turbulent wind noise

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Variables

• Road surface type and conditions
• Vehicle type and condition (passenger

vehicles, trucks, buses and motorcycles)

• Tire configuration
• Number of vehicles, vehicle speeds
• Engine load

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Levels

• Distance reduces noise — the further you are

away from the noise, the quieter it is

• 2x traffic volume results in a 3 dBA increase

(barely subjectively noticeable)

– Double the traffic volume does not result in double the noise

• 10x traffic volume results in a 10 dBA increase

(subjectively twice as loud)

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Current Noise Study

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Policy

Alberta Transportation Noise Attenuation Guidelines for Provincial Highways:

“For construction or improvements of highways through cities and other urban areas, Alberta Transportation will adopt a noise level of 65 dBA Leq24 measured 1.2 m above ground level and 2 m inside the property line (outside the highway right-of-way). The measurements should be adjusted to the 10-year planning horizon, as a threshold to consider noise mitigation measures.”

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Policy

• Noise levels are measured objectively (1.2 m

above ground level and 2 m inside the property line) to ensure all are treated fairly

• Alberta Transportation’s noise policy is similar to

that of the City of Edmonton

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Noise Study Purpose

• Initiated by Alberta Transportation (AT) based on

Ministerial commitment to conduct the study in 2016, prior to the original 2018 timeline.

• Current noise levels will be compared to 2007

and 2013 noise monitoring results, and against AT’s noise level guidelines.

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Noise Monitoring

• Where

– 13 locations throughout study area – Same locations as 2007 and 2013

• When

– 24-hour monitoring period – Downwind conditions – Four separate monitoring periods to cover all locations under appropriate wind conditions

23 87 Avenue Whitemud Drive 62 Avenue Lessard Road Rabbit Hill Road Terwillegar Road Calgary Trail 111 Street

= Noise Monitor

Study Area

Stony Plain Road

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Current Noise Study: Monitoring

• How

– dBA and frequency data recorded every 15 seconds – Simultaneous digital audio recording for “isolation” analysis – Portable weather monitoring station obtains accurate local meteorological conditions

• Why

– For the calibration and verification of the noise model

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Modelling

• Computer noise model of entire study area considers:

– Traffic on SW AHD, as well as all intersecting Edmonton roads and interchanges – Elevation contours – Residential property lines – Residential and commercial structures

• Noise levels are calculated at 1.2 m elevation, 2 m inside

property line

• Colour noise maps are calculated for entire study area
• Sensitivity analysis is created to account for fluctuations

in traffic volumes, heavy trucks, speed

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Noise Study Timeline

• Noise monitoring began a few weeks ago, however, due

to construction in the area, monitoring at all locations could not be completed.

• Next spring (as soon as weather permits) monitoring will

resume at all locations. Sites completed in 2016 will be redone to ensure a standardized baseline.

• Monitoring will take approximately 6 weeks to complete.
• Following monitoring, the noise modeling and analysis

will be completed. The final report is expected in late summer.